I am making a mustered cream sauce
You should be able to use whipping cream if the recipe calls for just "cream."
Half and half is just that--half milk and half cream. As said before, cream (whipping cream) is what us customarily used in sauces when cream is called for. Sauces don't thicken as well or have the same richness if you sub out half and half for cream --not that you were planning to!